Patent GB-433785-A (GB)
Title: Improvements in or relating to the treatment of cellulose esters
IPC: C08B3/22
Filed: 1934-02-16
Abstract: Cellulose triacetate is treated to modify its solubility by subjecting it to regulated heating in solid form, i.e. without first dissolving or suspending it in a liquid medium, with a substantial quantity of an alcohol having a swelling action or an alcohol having a solvent action on the triacetate to serve as retroacetylating agent thereof in the presence of a small amount of an esterifying catalyst such as phosphoric or sulphoric acid. Suitable alcohols having a swelling but no solvent action are ethyl, propyl, iso-butyl, amyl alcohols, or ethylene glycol, and when employing one of these, the treated cellulose ester may be separated from the reaction medium by mechanical means, the unreacted alcohol and the ester formed during the reaction being separated, e.g. by fractional distillation, and the alcohol and undistilled catalyst being used again.  Suitable alcohols having a definite solvent action are cyclo-hexanol or benzyl alcohol.  In this case the partially de-esterified cellulose acetate is recovered by precipitation by means of a non-aqueous medium miscible with the alcohol employed and the ester formed in the opening reaction, e.g. methyl alcohol or benzene.  The extent of the de-esterification is controlled by the time of treatment, the temperature and the nature of the alcohol and the catalyst.  In an example, 10 parts of cellulose triacetate were treated for 2 \ba1/2\be hours at 100 DEG  C. with 150 parts of normal butyl alcohol and 15 parts of orthophosphoric acid (80 per cent strength).  The separated acetate was substantially unchanged in acetyl value, was still insoluble in acetone, but its viscosity in methylene chloride was increased by about 20 per cent.  In other examples, 10 parts of cellulose triacetate were treated for 2 \ba1/2\be hours at 76 DEG  C. with 100 parts of ethyl alcohol, and 3 parts of nitric acid (67 per cent strength); for 10 hours at 93 DEG  C. with 100 parts of propyl alcohol and 8 parts of ortho-phosphoric acid (80 per cent strength); for 2 \ba1/2\be hours at 127 DEG  C. with 100 parts of amyl alcohol and 8 parts of ortho-phosphoric acid (80 per cent strength); or for 14 hours at 37 DEG  C. with 100 parts of benzyl alcohol and 1 part of concentrated sulphuric acid.  In each case after separation the acetate was found to be partially de-esterified, and to be soluble in acetone, but a film formed from a solution of it in acetone was no longer soluble in acetone. In further examples 10 parts of cellulose triacetate were treated for 2 hours at 94 DEG  C., with 100 parts of normal butyl alcohol and 3 parts of hydrochloric acid (33 per cent strength); for 45 hours at 40 DEG  C., with 100 parts of normal butyl alcohol and 2 parts of perchloric acid (20 per cent strength); for 3 hours at 90 DEG  C. with 66 parts of normal butyl alcohol, 34 parts of benzyl alcohol and 2 parts of nitric acid (67 per cent strength); or for 5 \ba1/2\be hours at 95 DEG  C. with 120 parts ethylene glycol and 10 parts phosphoric acid (80 per cent strength).  In each of these cases the acetate after separation was completely soluble in acetone. According to the Provisional Specification the process is not limited to cellulose triacetate, but includes other esters.